Production of regenerated cellulose yarn



ec. 23, 1941. E. A. TIPPETTS 2,257,955

, PRODUCTION OF REGENERATED CELLULOSE YARN I Filed June 10, 1939 '-;iia.

' 5222811901? A. ZE'ppeztJ INVENTOR jIWTORNEY Patented Dec. 1941 UNITEDSTATES PATENT oppmgfl Emerson A. Tippetts, Kenmore, N. Y., assignor toE. L du Pont de Nemours & Company, Wilmington, DeL, a corporation ofDelaware Application June 10, 1939, Serial No. 218,426

V 2Claims.

cellulose yarn is subjected to a stretching operation while in contactwith a liquid having an .ele-

vated temperature.

Heretofore, in the production of fine denier filament yarn by theviscose process it has been commercially uneconomical to produce yarnsthe filaments of which were finerthan about one denier per filament.Furthermore, the previously known processes for the production of suchone denier per-filament yarns were attended by difllculty of spinningand very material and objectionable yarn degradation.

It is an object of the present invention to produce, by the viscoseprocess, regenerated cellulose yarn composed of filaments having adenier of less than one.

It is another object of this invention to produce, by the viscoseprocess, regenerated cellulose yarn composed of filaments having adenier of the order of 0.5 to 0.75.

It is a further object of the present invention to provide a process forthe production of extremely fine denier filament regenerated celluloseyarn from viscose, which process represents an improvement in efliciencyand decreased filament degradation over previously known processes.

It is a. still further object of the present invention to provide aprocess for the production of extremely fine denier filament regeneratedcellulose yam from viscose by subjecting the previously regenerated yarnto a stretching operation while in contact with a liquid having anelevated temperature.

Other objects of the invention will appear hereinafter.

In accordance with the present invention, the

tained when the hot liquid bath is a hot sulfuricacid bath.

It has now been found that regenerated cellulose filaments having adenier of less than one, for example, having a denier of the order of0.5 to 0.75, can be spun from viscose if the freshly spun filaments,spun under low tension, are removed from the regenerating bathand passedinto a' stretching bath having a temperature of between 60 C. and theboiling temperature of the bath liquid, in which they are given amaterial stretch.

It has been discovered that very materialadvances in economy andmaterial reduction in yarn degradation will be obtained if the freshlyprecipitated fine denier filament yarns are stretched in a hot sulfuricacid bath, and if the contact-with the said hot sulfuric acid bath isconfined to a distance 01.45 inches or less based on spinning speeds of3000 to 8000 inches per with hot sulfuric acid during the stretchingoperation is critical, from a standpoint of yarn deg-. radation, whencompared with the prior art processes in which it was considerednecessary to contact the threads in hot liquids for a distance of 2 to12 meters (78 to 460 inches) at speeds considerably less than 3000inches per minute.

The procedure and apparatus by means of which'the process of the presentinventionmay be carried out will be clearly apparent from the followingdescription when taken in connection with the accompanying illustration.

The accompanying illustration is a diagrammatic perspective view of oneform of apparatus suitable for use in accordance with the presentinvention.

Referring to the illustration, reference numeral 7 H designates aspinneret which is positioned in tank I! containing a coagulating andregenerating bath l5. A viscose solution is extruded through spinneretll into bath l 5 for the formation of a multifilament yarn II. The yarnI1 is passed about pin, I! which functions as a convergence guide tobring the several extruded filaments together into .a single yarn. Theyarn is then passed about a plurality of roller guides 2|, thence aroundguide 23. After passing around guide 23 the yarn is drawn from thecoagulating and regenerating bath by means of transfer roller 25. Theyarn may be looped one or more times about the transfer roller 25 toprevent slippa e'of the yarn thereon. The yarn is then passed aroundrollers 33 which are submerged in a hot sulfuric acid bath 29 in tank21. The yarn is drawn from the hot sulfuric acid bath 29 and I pumpedinto the coagulating and regenerating bath l by means of pump 421 andconduit 39, or the hot acid bath may be drained through conduit 40.Spent coagulating and regenerating liquid may be passed from thecoagulating tank l3 through conduit 4 I.

It is to be understood that the illustrated and above-describedapparatus is disclosed for illustrative purposes only. Obviously variousdiiierent forms and modifications of apparatus can be employed equallywell.

The number and type of roller guides ii in the coagulating andregenerating bath will be determined by the spinning speed, by the sizeof the threads or filaments being spun, by the tension to be imposed onthe yarn, and by the composition of the coagulating and regeneratingbathliquid.

It is necessary to maintain sufiiciently low tension on the yarn duringits travel through the passed onto a collecting bobbin 35. The hot acidregenerating bath to allow sufllcient stretch to be from overlapping andchafing each other. The

transfer roller may be rotated by the pull exerted page 69.

To avoid w mer t will be understood to refer to the peripheral velocityof the spin-bobbin in the bobbin process or the feed wheel speed in thebucket process, and the term spinning tension" is the tension on theyarn, measured at a point just ahead of the spin-bobbin or itsequivalent, when the spinning containing approximately 7% cellulose and6% sodium hydroxide is used. Obviously viscose having differentcharacteristics can be employed in the practice of the inventiondepending upon the type of yarn to be produced. Particularly goodresults have been obtained by the use of a viscose spinning solutionwhich has been ripened to a point where it has an index materiallygreater than 4.0, for example an index of 4.5 to 6.0, or even greater,as determined by the-method of Reinthaler and Rowe, fArtificial Silk}!.--1928,

Example! Viscose is passed through a spinneret containing 100 holes,with an average viscose delivery of 7.7 grams per minute, intoanaqueousspinning bath containing 9% sulfuric-g'acid, 19%"scdiumsulfate, 4% glucose and 0.85%{z'inc suimtegsam bath being maintained atiI-L-1 C. The extruded filaments are. guided through this bath by aplurality of roller guides selected tempos-e a slight tension onth'e'yam' bath' 't'ravei of 26 inches. The yarn is withdrawn'from thebath and passed overa; "yarn drlventransfer roller into a secondary bathwhich" consistsbf an aqueous solution containing 2% S 111furicacid'andwhich is maintained at 'a temperature of 90i2 C. The yarn is guidedthrough the secondary thereon by the yarn, or the roller may be posi- 5tively driven in any desired manner. The collecting bobbin may be of anytype well known in the art. The collecting bobbin will, of course, beprovided with necessary traverse guides in a manner well known in theart. If desired, the 'yarn may be drawn through the hot acid bath 29 bymeans of a feed roll or the like and collected ina rotating bucket inaccordance with theconventional bucket process for the production ofrayon yarn. In any event, the collecting bobbin, or the feed roller whenusing the bucket process, will be rotated at a peripheral speedsufllciently higher than the peripheral speed of transfer roller 25 toimpart a stretch to the yarn as it passes through the hot acid bath 29.The stretch imposed on the yarn in the bath 29 may be as low as 5% or10%: however, to obtain the greatest benefit from the present inventionthe stretch imposed should be 30% to 60% or even 100% or more. dependingupon the tension imposed in the spinning bath. upon the physicalcharacteristics to be imparted to the yarn, and limited by the stretchthe yarn will stand without breaking.

The spent coagulating and regenerating liquid mav be discarded, or itmay be renovated, as desired.

For convenience the invention will be described in terms of a spinningprocess as depicted in the drawing where the yarn is collected on aspinhnbbin.

bath by a plurality of roller'guide's selected so that at a spinningspeed of 4500 inches per minute the spin tension will be 29"grams whenthe peripheral speed of the yarn driven f-transfer roller is 3040 inchesper minute. The finished yarn, after washing on thebobbinor'l 'which ithas been collected, and twister drying' 'inaccordance with themethod'describ'ed 'in- Parker Example II I Viscose is passed through-aspinneret-containlng holes, with an .average'viscosedelivery of 11 gramsper minute, into an aqueous spinning bath containing 11% sulfuric acid,23%,sodiuigi sulfate, 4%- glucose and 0.7% zincsulfatasaid bath beingmaintained at 45':1 C. ;The,-,extruded filaments are guided-through thebath; by a plurality oi roller guides selected toimpose a tension on theyarnduring a-bath travel of inches. The yarn is then led overa-freelyrotating transfer roller into a secondary bat wheel, whence itis collected .in. a centrifugal 1 bucket rotating at 10,000 R. P. M. inthe usual way. The spinning speed (feed wheel speed) is 3600 inches perminute and the roller guides in .the baths are such that a spin tensionof 85 grams is obtained when the transfer roll runs at a peripheralspeed of 2710 inches per minute.

Thefinishedyarmwashedanddriedinthe cake without bleaching, has a denierof about 100, (one denier per filament) a dry tenacity of 2.96 grams perdenier, and a wet tenacity'of 1.95

grams per denier with dry and 'wet elongations of 14.9% and 15.3%respectively;

By reference to the above examples, it will be apparent that yarn ofexceptionally fine denier can be produced from viscose with great caseeven though very highspinning speeds are employed. Yarn produced inaccordance with the present invention will have a high tenacity and maytherefore be used to greatadvantage in the production of sheer knitgoods and light-weight woven fabrics. The quality of the yarn is vastlysuperior to that of fine denier viscose rayon produced in prior artprocesses in respect to yarn degradation, yamtenacity and fineness ofdenier. The reason for this lies in the fact that the yarn denier can bereduced by a stretching operation in which much greater stretch can besecured than when stretching in the spinning bath is relied upon. Theamount of stretch given the yarn aifects in large measure the tenacityand denier of the final product; however, the stretch must be imposed onthe yarn during a comparatively short period so as to prevent yarndegradation. It material yarn degradation takes place the tenacity ofthe yarn will be substantially lowered.

The composition of the hot acid stretching bath may bethe same as thatof the coagulating and regenerating bath with the attendant advantagesof simplified bath make-up systems, use of hot bath overflow tomaintainspinning bath temperature and composition, economical use ultimately asspinning bath, and the like. However,'if high salt concentrations areused, the tendency toward crystallization in the hot acid stretchingbath is increased so that it is frequently preferabl to use a difierenthot bath composition. To this end then, compositions containing 2% to13% sulfuric acid, 0 to sodium sulfate and with or without zinc sulfateor glucose may be used. Inasmuch as the higher temperature of thesecondary bath is conducive to carbonization of glucose, a glucose-freebath' the spinning bath controls to a considerable extent the amount ofstretch which .can later be given the yarn in the hot acid bath- Thisrelationship is qualitatively expressed in the follow.- ingtable inwhich the tension ismeasured on the yarn as it leaves the spinningbathz' Tension stretch Per c0255 0.1gramper denier 0.4 grams per denier35 0.5 grams per denier 28 0.9 grams per denier 19 Thus it is readilyapparent. that since a relatively large amount of stretch is essentialwhen fine denier filaments are to be made it is advantageous to keep thetension on the, yarn in the spinning bath at a low level. The tension onthe yarn in the spinning bath must be maintained below 1.0 gram perdenier, and to obtain full advantage of the present inventionvthetension in the said spinning bath should not exceed 0.5 gram per denier.V y

.By the process of the present invention it is practical to'spin a yarnof 0.5 to 0.75 denier per filament at high speed while stillkeeping theyarn speed in the coagulating and regenerating bath sufliciently low to'prevent entrance of this bath into the spinneret, which will result inplugged spinneret holes. As a consequencespinnerets of larger hole sizescan be used than ha beenv possible, in prior art processes.

The ratio of spinning speed to average linear spin a 0.5 D/F yarn withsuch a spinventionwill permitratios of 6 or higher by virtue of a30%-60% or higher stretch imposed on the may be preferred. Inasmuch asgreater stretch temperature of the secondary bath is selected in therange of C. to boiling temperature, and

usually 90-100 C. This preferred range gen-- 'erally yields higherbreaking tensions, that is,

subjected the tensionto which athread can be before breaking.

yarn during its passage through the bath by virtue of the hot treatmentunder tension which in turn allows for slower yarn speeds in thespinning bath than can be possible in the absence of the hot bathtreatment.

The advantages'of the foregoing can be appreciated by the following. Inspinning fine denier per filament yarn the ratio of yarn speed, at apoint, say, 25 inches from the spinneret, to viscose delivery iscritical. For producing 1 D/F yarn by a single bath process this ratiois about 2.5 when a spinneret having holes about -0.0025 inch indiameter is used. Any decrease in filament denier without change in holesize will raise this ratio proportionately so that it will be about 5for a 0.5 D/F yarn. By theprocess of this invention the ratio can bekept well below 5 or in the range 2.9 to about 4. Similarly, for a yarnor 1 D/F, this invention makes it'possible to keep the ratio well below2.5 or in the range 1.5 to about 2. These lower ratios are valuable inproducing higher quality yarns by an economical procedure.

Since it is obvious that manychanges and v I 3 Theamount of tensionimposed on the yamin Breaking invention above described, it is to beunderstood that the invention is not to be limited except as set forthin the appended claims.

I claim: v

l. The process of spinning regenerated cellulose yarn comprisingfilaments having a denier of less than one which comprises extruding aviscose solution into a coagulating and regenerating bath the diluteacid type (of the order 01' 9% to 11% acid) with a ratio of'yarn speed,at a point 25 inches from the spinneret, to viscose delivery speed 012.9to 4 (based on a 0.5 denier per filament yarn) to form yarns,maintaining said yarn under tension of lessthan 1 gram per denier duringits passage through said coagulating and regenerating bath, removingsaid yarns from said bath and passing them, for a distance not to exceed45 inches, based on a spinning speed of 3000 to 8000 inches per minute,through.

a 2% to 13% sulfuric acid bath having a temperature of 60 C. to boilingtemperature, and

stretching said yarns at least 30% to materially reduce their denierduring their passage through said hot acid bath. c

, 2,207,055 modifications can be made in the details of the 2. Theprocess of spinning regenerated cellulose yarn comprising filamentshaving a denier denier during its passage through said coagulating andregenerating bath, removing said yarns from said bath and passing them,for a distance not to exceed 45 inches, based on a spinning speed of3000 to 8000 inches per minute, through a 2% to 13% sulturic acidbath'oi a composition essentially the same as said coagulating andregenerating bath and having a temperature of 60 C. to boilingtemperature, and stretching said yarns at least to materially reducetheir denier during their passage through said hot acid bath.

' EMERSON A.- TIBPE'I'IS.

